This invention relates to a process for the production of rigid and semi-rigid foams at low isocyanate levels, and to the foams produced by this process. The process comprises reacting a polyisocyanate component with an isocyanate-reactive component, in the presence of at least one blowing agent, at least one surfactant and at least one catalyst. Suitable isocyanate-reactive components are characterized as having a solids content of at least 40% by weight, and an overall hydroxyl number of the remaining liquid, non-solids portion of at least 160. In addition, the isocyanate-reactive component comprises at least 50% by weight of a polymer polyol having a solids content of at least 30% by weight and in which the base polyol has a hydroxyl number of at least 70.
Rigid and semi-rigid foams find use in packaging and in other energy management applications such as energy dissipating foams for automotive applications. They are also used to provide support and impart stiffness in various composite constructions such as automotive headliners and various sandwich structures.
Energy absorbing foams are known and disclosed in the art. See, for example, U.S. Pat. Nos. 6,265,457 and 6,777,457.
The energy-absorbing foams of WO 98/16567 comprise 100 parts by weight of an isocyanate-reactive component that consists of (a) 30 to 70 parts by weight of a polyol having a molecular weight of 2500 to 6500, a functionality of 2.5 to 6 and a primary hydroxyl content of at least 40% by weight, and which optionally contains a polymer stably dispersed in the polyol, with (b) 70 to 30 parts by weight of a rigid polyol having a molecular weight of 300 to 1000, a functionality of 2.5 to 6 and a hydroxyl value in the range of 200 to 600. This isocyanate-reactive component makes it possible to prepare foams having a density of less than 50 kg/m3.
U.S. Pat. Nos. 6,265,457 and 6,777,457 describe isocyanate-based polymer foams which comprise an isocyanate-based polymer matrix having a crystalline particulate material disposed in the matrix. The process for producing these foams comprises contacting an isocyanate, an active hydrogen containing compound, water, and a particulate material having an enthalpy of endothermic phase transition of at least about 50 J/g to produce a reaction mixture, and expanding the reaction mixture to form the isocyanate-based polymer foam.
Rigid polyurethane slab foams and the process for the preparation are disclosed in JP 05186559. These comprise the reaction of NCO-terminated prepolymers of rigid polyols and TDI or polymeric MDI, and rigid polyols containing 10 to 100 parts of polyether polyols prepared by alkoxylating trimethylolpropane, and a blowing agent comprising dichlorotriflurorethane.
Thermoformable flexible polyurethane and their use as packaging materials is known and described. See the paper by S. E. Wujcik et al titled “Thermoformable Flexible Polyurethane: A Unique Packaging Material”, presented at the 32nd Annual Polyurethane Technical Marketing Conference, Oct. 1-4, 1999, pp. 223-226. The foams described in this paper also have excellent energy absorbing characteristics, and allow cushioning products to be tailored to detailed specifications required for protection of a wide variety of parts over a broad environmental spectrum. These polyurethane foams are prepared from MDI or TDI, with a new graft polyol (i.e. Pluracol® Polyol 1150) and have improved compressive strength. TDI foams having 50% compressive strengths up to 5.2 psi at a density of 2.1 pcf are described. An MDI foam with 50% compressive strength of 12 psi and a density of 2.0 pcf is also described, but no information about the MDI level is provided.
Advantages of the present invention include production of rigid and semi-rigid foams exhibiting increased compressive strength as a function of density when produced. In particular, high compressive strength foams of lower density can be produced with lower isocyanate reactant levels and lower heat generation during the production process. This is particularly beneficial in avoiding exothermic decomposition and even fire in the production of large foam buns via a one-shot slabstock or box foaming process. The process also enables the use of isocyanates or isocyanate blends having higher free NCO content including TDI which is available in many foam production facilities. The production flexibility provided by the use of TDI and the use of less isocyanate may also help overcome restrictions on rigid and semi-rigid foam production caused by temporary or longer-termed shortages of isocyanates of higher free NCO or of isocyanate chemicals overall.